Process of forming double nitrids.



UNETED STATE YFATENT SAMUEL PEACOCK, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, T0 'AGRICULTURAL RESEARCH CORPQRATION, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

PROCESS OF FORMING DOUBLE NITRIIDS,

No Drawing.

To all u-lzom it may concern:

Be it known that I, SAMUEL 1)I'1ACO(K, a citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Processes of Forming Double Nitrids;-and I do hereby declare the following to be a full, clear, and exact description. of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to a process of fixing atmospheric nitrogen, and has for its object to chemically fix such nitrogen in an expeditious and comparatively inexpensive manner. I

To these ends the invention consists in the steps and combinations of steps more fully hereinafter disclosed and particularly pointed out in'the claims by which nitrogen is chemically combined with a metal and with a non-metallic element or with two metals to form a double nitrid, as will now be explained. v i

In the )rocess of making silicon carbonitrid .(Si N I observed that the temperature of the formation of the double nitrid is so nearly that of its dissociation, hat the process of producing the latter became one of exceptional refinement in carrying it out. I discovered, however, upon usinga mixture ofcalcium oXid, and aluminum oXid or of other-oxids; with the silica and carbon, the range of difference between the temperature of formation and dissociation was sulli- .ciently increased to materially lessen the need of an exceptionately accurate control of the furnace temperatures. This led me to the further discovery that it was practical to tix atmospheric nitrogen by means of double nitrids ot' a metal and a non-metal in which silicids or silicon carbids are utilized, and thus produce compounds such as as well as-other like compounds in which other metals may be substituted for those mentioned. in other words. ll discovered that it was possible to substitute silicon tor carbon in the older processes it mctal osids were mixed with the charge of carbon and silica.

Patented Sept. 28, 1915.v

Application filed May 31. 1913. Serial No. 770.933.

Incarrying out my process, I provide a IlllXtUl'Q of carbon, silica and an oxid of a metal. using either a natural compound such as feldspar, or a mixture of oxids in such proportions that the e will be present in the charge 'sutticient carbon to effect the reduction of substantially all the silica present, and to cause the formation of the higher carbid of silicon Sit") This latter arbid is not yerystable at the tenmerature of its formation, but it readilyreacts with alumina, calcium oXid, etc.. to form silicids in accordance with the following:

These reactions, (or similar'reactions in which other metals are substitute: for the aluminum, calcium or potassium) are by my process etlcctcd in an. atmosphere of nitrogen. swam, the metal silicids produced being unstable, ordinarily tend to break down, substantially as follows,

I lind those resulting doublc nitrids are quite stable over a temperature range so wide as to eliminate troublesome furnace control refinements in practical furnace operations and that the zinc carbid Zui is a very useful one to employ in the beginning. Accordingly, in the operation of my process I take the required mixture of carbon, metal oxids, and silica, as separate sub; stances, or any natural or artificial compound or mixture of the same, and h art such mixture by any suitable means in an atmosphere of nitrogen. Preferably, l cake or briquet the mixture, and make use of a producer gas containing a low percentage of carbon dioxid as a source of nitrogen; the said producer gas being passed, over or through the cakes or mixture as the same is heated. lhe temperature required is from 1600 to 2000 C. depending upon the velocity with which the producer gas is passed through or over the furnace mixture. The first step in the reaction produces carbon monoxid CO as a gaseous reaction product, and the reaction velocity is governed by the partial pressure of this said carbon mon oxid that is allowed to exist in the furnace atmosphere; hence, in order to hasten this velocity and at the same time increase the above range of temperature differences, I keep the partial pressure of this gaseous reaction product as low as possible as by sweeping the producer gas somewhat rapidly through or over the charge in the furnace under treatment.

I preferably use any suitable furnace employing e ectricity having opposed electrodes as a. source of'heat, and provided with suitable well known devices for a continuous feeding of the charge and for the removal of the furnace product.

In carrying out the above process I have found evidences of a nitrogen compound corresponding to the formula Al,N,.Si,,N but could not prove it to be anything more than a mixture of the two compounds Ahll and S1 N which may have resulted from excessive ten'iperatures' in particular portions of the furnace. However, although such compounds are included 111 my d1scovery, yet it is important to avoid the formation of such compounds or mixtures, because they require a greater expenditure of energy, and fix a much less quantity of nitrogen than do the higher nitrids. Such avoidance can be accomplished by watching the operation, and seeing that the temperatures are as even as possible all over the reaction. zone.

In making up the furnace. charge 1 find a desirable mixture to consist in feldspar and phosphate rock in such proportions that the silica of the feldspar-is supplied with ample calcium oxid from the phosphate rock to form the above calcium silicid, for in such case not only is the silica, alumina and 7 calcium oxid of the minerals thus utilized to fix nitrogen, but the potassi Inn of the teldspar, and the phosphorus ol the phosphate rock are first both volatilixcd in the form 01 oxids, and then converted into carho-nitrids and carbids. in this latter form they may be treated with hot water under pressure and converted into phosphoric acid, potassium oxid and ammonium salts, thus forming valuable b v-products.

It will be cl ar from the foregoing that the above various reactions, illustrated with the use of a higher -.arbid of silicon, SiU take place simultaneously or successively in the furnace until the final double nitrid is formed, and it should also be observed that it is important to form or employ this particular class of higher carbids, for it is these same higher carbids that are found to effect the dissociation in the cyanamid process of fixing nitrogen. Such higher carbids are SiC ZnC, A1 0 CaC. They invariably give rise in the reaction to a carbon valency corresponding to C H and this said valency will cause for example the compound AIQL. "i,,N,, to be produced if the temperature is not too high instead of the compound Al,N .Si ,N Of course, it such higher carbids as ZnC, Al G CaC, etc., are substi tuted for the silicon carbid SiC in the above reactions, then the double nitrids produced will be correspondingly changed. In other words, in the presence of nitrogen I may employ two oxids of metals, instead of an oxid of a metal, and an oxid of a non-metal, and produce the above higher carbids of the metals during the reaction, which will immediately break down, and give rise to double nitrids of the corresponding metals present, instead elf-double nitrids of a metal and a nonmetal.

It is obvious that those skilled in the art may vary the steps without departing from the spirit of myinvention, and therefore I do not wish to be limited tot-he above disclosure except as may be required by the clain'is.

\Vhat I claim is 1. The process of fixing atmospheric nitrogen which consists in heating in the presence oi said nitrogen a suitable oxid mixed with a higher carbid and to a teumerature suflicient to produce a double nitrid, substantially as described.

2. The. process of fixing atmospheric nitrogen which consists in heating in an atmosphere containing said nitrogen, an oxid mixed with a higher carbid of a non-metal and to a temperature suilicient to produce av double nitrid containingsaid non-metal, substantially as (lQSCI'lbOt.

3. The process of fixing atmospheric nitrogen which consists in providing a mixture of silica, a suitable oxid and carbon; and heating said mixture in an atmosphere of nitrogen to a, temperature suli'iciont to first form a higher carbid of silicon, and then to form a double nitrid containing silicon, substantially as described.

4. 'lheprM-essol' fixing atmospheric nitrogen'which consists in providing a mixture of silica, calcium oxid and carbon; and heating said mixturetto atemperature'sufiicient to produce a double nitrid. of calcium and silicon, substantially as described.

The process of fixing atmospheric Intro- 'gcu which consists in heating in the presence;

of said nitrogen a suitable oxid mixed with 1 a higher carbid to a temperature sufficient toproduce a'double nitrid, while sweeping ble nitrid while sweepin said nitrogen'over SiIId mixture to reduce the partial pressure of the evolved carbon monoxid gas substantially as described.

M 7. The process offixing atmospheric nitrogen which consists in providing a mixture to produce a double said nitrogen, a sultable ofsilica, a suitable oxid and carbon; and

heating-said mixture in an atmosphere of nitrogen to a temperature suflicient to first form ahigher carbid of silicon, and then to form a double nitrid-while reducing the normal partial pressure of the evolved gaseous reaction products, substantially as described.

8. The process of fixing atmospheric nitrogen which consists in providing a'mixture" of silica, calcium oxid 111g said mixture to 'a and carbon; and heattemperature SllfllQlBllt SAMUEL PEACOCK. Witnesses:

Enw. JANES,

' F. A. Wlcrmmsroo'iv. I

nitrid of calcium and silicon while reducing the partial pressure of the evolved carbon monoxid.gas,:substan- 'tially as described." j In testimony whereof I affix my signature, in presence of two Witnesses. 

